Name: ester formation and everyday fragrances
Uploaded: 2020-03-26T07:22:29.000Z
Duration: 3 min 48 s
Channel: JoVE

K12 Standards

Florida Department of Education

High School

Physical Science

SC.912.P.8

SC.912.P.8.13

Esterification

Gli esteri sono una classe di molecole organiche che possono avere un aroma fruttato o floreale. La struttura di un estere è un carbonile con un gruppo alchilico o arilico su un lato e un ossigeno legato a un altro gruppo alchilico o arilico sull'altro lato.
A seconda dei gruppi alchilici o arilici, l'estere può assumere molte caratteristiche diverse. Ad esempio, la reazione del glicerolo e di tre acidi grassi, che sono acidi carbossilici con lunghe catene alchiliche, si traduce in un trigliceride, che ha tre gruppi estere. Le lunghe catene alchiliche degli acidi grassi conferiscono ai trigliceridi un peso molecolare molto elevato. Al contrario, gli esteri semplici hanno un basso peso molecolare e piccoli gruppi funzionali.
Gli odori e i sapori di frutta e fiori sono attribuiti a semplici esteri. Anche piccoli cambiamenti nella struttura di un estere semplice influenzano notevolmente la sua fragranza. Ad esempio, cambiando un gruppo ossidrile in un'ammina cambia il profumo di questo estere da wintergreen a uva. Allo stesso modo, l'acetato di propile odora di pera, mentre l'acetato di butile, che ha solo un altro carbonio nella sua catena, odora di mele.
Un modo comune per produrre un estere è l'esterificazione di Fischer, in cui un acido carbossilico e un alcol reagiscono in presenza di un catalizzatore acido per formare l'estere e l'acqua. Il gruppo R e il carbonile provengono dall'acido carbossilico, e il gruppo alcossi o arilossi con la R' proviene dall'alcol. Questa reazione di esterificazione è reversibile. Con una miscela 1 a 1 dell'acido carbossilico e dell'alcol, tende a raggiungere l'equilibrio con una resa di circa il 70% dell'estere nella migliore delle ipotesi.
Tuttavia, il principio di Le Chatelier ci permette di aumentare la resa dell'estere oltre a questo. Il principio di Le Chatelier afferma che qualsiasi sistema in equilibrio chimico soggetto a un cambiamento di concentrazione, pressione, temperatura o volume si adatterà a un nuovo equilibrio che contrasta il cambiamento.
Quindi, se aumentiamo la concentrazione di uno dei reagenti in una reazione reversibile, l'equilibrio si sposterà nella direzione che diminuisce la sua concentrazione. Ciò si traduce in una maggiore resa del prodotto estere all'equilibrio. Pertanto, possiamo migliorare la resa dell'esterificazione utilizzando un rapporto molare 3:1 o 1:3 tra acido carbossilico e alcol.
In questo esperimento, verrà eseguita un'esterificazione di Fischer utilizzando alcol in eccesso e acido solforico come catalizzatore. In questa reazione, la reattività dell'acido carbossilico è potenziata dall'acido solforico, che protona l'ossigeno del carbonile. L'alcol è un nucleofilo che attacca il carbonio del carbonile per formare un intermedio. Successivamente, l'idrogeno dell'alcol viene trasferito in un idrossile vicino. Il carbonile quindi si riforma, eliminando una molecola d'acqua. Infine, la deprotonazione si traduce in un estere neutro.
In questo laboratorio, eseguirai una reazione di esterificazione di Fischer con un alcol sconosciuto e un acido carbossilico in un rapporto molare di 3:1. Identificherai quindi l'estere usando il suo odore, determinerai la resa e identificherai i due reagenti sconosciuti in base alla struttura dell'estere.

esterificazione

<h4>esteri</h4>
La struttura di un estere è un carbonile con un gruppo alchilico o arilico (R) da un lato e un ossigeno legato a un altro gruppo alchilico o arilico (R') dall'altro lato, rappresentato dalla formula generale: RCOOR'. Gli esteri possono essere comunemente derivati da una reazione di esterificazione tra un acido carbossilico e un alcol. Il gruppo ossidrile dell'acido carbossilico è sostituito da un gruppo alchilico o arilico. Gli esteri semplici, che hanno un basso peso molecolare e piccoli gruppi funzionali R e R', hanno odori e sapori di frutta e fiori.
L'acido carbossilico più semplice è l'acido formico (HCOOH), mentre l'alcol più semplice è il metanolo. Pertanto, l'estere più semplice formato dall'esterificazione di queste due molecole è il formiato di metile (HCOOCH3). Il formiato di metile è considerato un derivato dell'acido formico perché il gruppo OH è sostituito dal gruppo OCH3. Le differenze strutturali tra il formiato di metile e l'acido formico determinano la differenza nelle loro proprietà. Questo perché le proprietà della molecola dipendono fortemente dai gruppi R e R'.
Gli esteri che si trovano nei frutti e nei fiori sono noti come esteri semplici a causa della bassa complessità della loro struttura rispetto ad altri esteri. I gruppi alchilici e arilici presenti su questi esteri influenzano notevolmente la fragranza che emettono; Pertanto, l'aggiunta di un carbonio o di un diverso gruppo funzionale può influire sul profumo prodotto dall'estere. Ad esempio, l'acetato di propile (C5H10O2) ha il profumo delle pere. Tuttavia, l'acetato di butile (C6H12O2), che ha solo un altro carbonio nella sua catena, odora di mela.
Gli esteri a catena lunga, ovvero quelli con lunghe catene alchiliche, sono chiamati acidi grassi. Gli acidi grassi sono importanti composti biologici essenziali per alcuni processi biologici. Gli acidi grassi sono anche una forma biologica di accumulo di energia. Quando tre acidi grassi reagiscono con il glicerolo, formano un trigliceride, la forma più comune di acidi grassi. I trigliceridi hanno un peso molecolare molto elevato e possono essere molto ramificati. La loro funzione e le loro proprietà dipendono dalla lunghezza e dai tipi di catene alchiliche incorporate nella loro struttura. Uno degli usi industriali più comuni dei trigliceridi è nella produzione di saponi e detergenti.
<h4>Reazione di esterificazione</h4>
Gli esteri si formano da una reazione di esterificazione, mentre gli esteri semplici si formano attraverso l'esterificazione di Fisher. Questa reazione converte un acido carbossilico e un alcol in un estere con acqua come sottoprodotto. L'esterificazione di Fisher è una reazione reversibile che procede molto lentamente. Un catalizzatore acido, tipicamente sotto forma di acido solforico, viene aggiunto per aumentare la velocità della reazione e allo stesso tempo fungere da agente disidratante.
Il meccanismo d'azione per un'esterificazione di Fisher inizia con l'ossigeno carbonilico che attacca l'acido solforico e deprotona il suo gruppo OH. Questo porta a un ossigeno carbonilico caricato positivamente. Per stabilizzare meglio la carica positiva, una coppia di elettroni del doppio legame carbonilico viene spinta verso l'ossigeno carbonilico, creando contemporaneamente un centro di carbonio povero di elettroni. Successivamente, il gruppo idrossilato dell'alcol agisce come un nucleofilo e attacca il carbonio povero di elettroni - l'elettrofilo - formando un intermedio. Quindi, il gruppo ossidrile caricato positivamente dell'alcol viene deprotonato dal gruppo ossidrile dell'acido carbossilico, stabilizzando l'atomo di ossigeno dell'alcol. Nell'ultimo passaggio, l'ossigeno carbonilico viene deprotonato dalla base coniugata e la coppia di elettroni liberi viene spostata verso il centro carbonilico mentre il gruppo carbossilico protonato esce come molecola d'acqua.
Poiché la reazione di esterificazione è reversibile, una miscela 1:1 dell'acido carbossilico e dell'alcol raggiungerà l'equilibrio con una resa di circa il 70% dell'estere. Tuttavia, come con qualsiasi processo di equilibrio, la reazione può essere guidata in una direzione modificando la concentrazione, la pressione, la temperatura o il volume dei reagenti. Questo cambiamento fa sì che la reazione si adatti a un nuovo equilibrio per contrastare il cambiamento, che è alla base del principio di Le Chatelier.
Quando la concentrazione di uno dei reagenti viene aumentata, l'equilibrio si sposta nella direzione che diminuirà la sua concentrazione. Pertanto, aumentando la concentrazione di un reagente, l'equilibrio produce più prodotto, determinando così una maggiore resa del prodotto estere.
Un metodo comune utilizzato nei laboratori di chimica organica è quello di fornire un eccesso di uno dei reagenti, in genere l'alcol. Come accennato in precedenza, l'esterificazione di Fisher può utilizzare l'acido solforico come catalizzatore. Tuttavia, una delle altre funzioni dell'acido solforico è quella di agire come agente disidratante, sequestrando le molecole d'acqua lontano dalla reazione. L'applicazione del principio di Le Chatelier dimostra che quando uno dei prodotti viene rimosso – in questo caso, l'acqua – la reazione è spinta a produrre più prodotto. Ciò aumenta la resa dell'estere formato.
<h4>riferimento</h4>
<ol>
	<li style="font-size:17px">Streitwieser, A., Heathcock, C.H., Kosower, E.M. (1998). Introduzione alla Chimica Organica. Upper Saddle River, NJ: Prentice Hall.</li>
</ol>

Esterificazione

Esteri
La struttura di un estere è un carbonile con un gruppo alchilico o arilico (R) su un lato e un ossigeno legato a un altro gruppo alchilico o arilico (R') ...

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ester formation and everyday fragrances

Esters are organic compounds with a carbonyl group attached to an oxygen that connects to another alkyl or aryl group. Their general formula is RCOOR'. They are often made by reacting a carboxylic acid with an alcohol in an esterification reaction. In this process, the hydroxyl group of the acid is replaced by an alkyl or aryl group.

Many simple esters have familiar fruit and flower smells because their structures are small and less complex. Formic acid and methanol can combine to form methyl formate, the simplest ester from these two molecules. Methyl formate is a derivative of formic acid because the OH group is replaced by OCH3. Small changes in the R and R' groups can also change the properties and scent of an ester.

This is why similar esters can smell different. Propyl acetate has a pear-like scent, while butyl acetate smells like apples, even though the molecules differ by only one carbon. Long-chain esters are called fatty acids. They are important in biology and also serve as a form of energy storage.

When three fatty acids react with glycerol, they form a triglyceride. Triglycerides are the most common form of fatty acids and have a high molecular weight. They can also be highly branched. Their function and properties depend on the length and type of alkyl chains in their structure. Triglycerides are widely used in industry, including the production of soaps and detergents.

Simple esters are often made by Fischer esterification, which is a slow and reversible reaction. It converts a carboxylic acid and an alcohol into an ester and water. Sulfuric acid is commonly used as an acid catalyst. It speeds up the reaction and also acts as a dehydrating agent.

The reaction mechanism starts when the carbonyl oxygen interacts with sulfuric acid and becomes positively charged. The carbonyl double bond then shifts electron density toward the oxygen, leaving the carbonyl carbon more electron-poor. Next, the alcohol acts as a nucleophile and attacks that carbon, forming an intermediate. The alcohol oxygen is then deprotonated, and the carbonyl oxygen is finally deprotonated as water leaves.

Because Fischer esterification is reversible, a 1:1 mixture of the acid and alcohol reaches equilibrium at about 70% ester yield. The reaction can be pushed toward more ester by changing concentration, pressure, temperature, or volume. This follows Le Chatelier's principle, which says a system shifts to counter a change. In the lab, using excess alcohol is a common way to increase yield. Sulfuric acid also helps by removing water, and taking away this product drives the reaction to make more ester.

Ester Formation and Everyday Fragrances

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Video completi e incentrati sul curriculum sia per gli istruttori che per gli studenti nei corsi di laboratorio di Chimica introduttiva.

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Learn how carboxylic acids and alcohols form esters, why some smell fruity, and how Fischer esterification uses sulfuric acid to boost yield.

Ester Formation and Everyday Fragrances | JoVE K12

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Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

Heating and Cooling Curves

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance ...

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

SC.912.P.8.2

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

The Wave Nature of Light

The nature of light has been a subject of inquiry since antiquity. In the seventeenth century, Isaac Newton performed experiments with lenses and prisms ...

The Electromagnetic Spectrum

The electromagnetic spectrum consists of all the types of electromagnetic radiation arranged according to their frequency and wavelength. Each of the ...

Interference and Diffraction

Interference is a characteristic phenomenon exhibited by waves. When two electromagnetic waves interact with their peaks and troughs coinciding, a ...

Photoelectric Effect

When light of a particular wavelength strikes a metal surface, electrons are emitted. This is called the photoelectric effect. The minimum frequency of ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

Emission Spectra

When solids, liquids, or condensed gases are heated sufficiently, they radiate some of the excess energy as light. Photons produced in this manner have a ...

The de Broglie Wavelength

In the macroscopic world, objects that are large enough to be seen by the naked eye follow the rules of classical physics. A billiard ball moving on a ...

The Uncertainty Principle

Werner Heisenberg considered the limits of how accurately one can measure properties of an electron or other microscopic particles. He determined that ...

The Quantum-Mechanical Model of an Atom

Shortly after de Broglie published his ideas that the electron in a hydrogen atom could be better thought of as being a circular standing wave instead of ...

Explore the scientific theory of atoms (also known as atomic theory) by describing changes in the atomic model over time and why those changes were necessitated by experimental evidence.

SC.912.P.8.3

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Ions and Ionic Charges

In ordinary chemical reactions, the nucleus &mdash; which contains the protons and neutrons of each atom and thus identifies the element &mdash; remains ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Atomic Number and Mass Number

The number of protons in the nucleus of an atom is its atomic number (Z). This is the defining trait of an element. Its value determines the identity of ...

Explore the scientific theory of atoms (also known as atomic theory) by describing the structure of atoms in terms of protons, neutrons and electrons, and differentiate among these particles in terms of their mass, electrical charges and locations within the atom.

SC.912.P.8.4

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

Electron Configurations

Electron configurations and orbital diagrams can be determined by applying the Aufbau principle (each added electron occupies the subshell of lowest ...

Electronic Structure of Atoms


An atom comprises protons and neutrons, which are contained inside the dense, central&#160;core called the nucleus, with electrons present around the ...

Relate properties of atoms and their position in the periodic table to the arrangement of their electrons.

SC.912.P.8.5

A. A working definition of matter is that it takes up space, has mass, and has measurable properties. Matter is comprised of atomic, subatomic, and elementary particles.

B. Electrons are key to defining chemical and some physical properties, reactivity, and molecular structures. Repeating (periodic) patterns of physical and chemical properties occur among elements that define groups of elements with similar properties. The periodic table displays the repeating patterns, which are related to the atom's outermost electrons. Atoms bond with each other to form compounds.

C. In a chemical reaction, one or more reactants are transformed into one or more new products. Many factors shape the nature of products and the rates of reaction. 

D. Carbon-based compounds are building-blocks of known life forms on earth and numerous useful natural and synthetic products.

Ester Formation and Everyday Fragrances

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